The present invention relates to a tape measure which is capable of winding a measuring strip on a spring-driven reel in a housing.
Measuring strips made of steel, cloth, plastics or other material have been used for measurement of a length and a distance. Any conventional measuring strip is wound manually or automatically into a housing. A measuring strip of a self-winding tape measure has a concave sectional form and has the property of straightening itself when it is drawn out of the housing. A winding reel with a spring drive is used as a winding mechanism of the self-winding tape measure. Automatic winding of the measuring strip is performed by reversing the reel in the housing by the action of the spring whose force for returning to its original shape is stored while the measuring strip is drawn out of the housing.
The thus constructed winding mechanism of the self-winding tape measure uses a strong spring that can completely wind a measuring strip on the winding reel overcoming a friction force, and can also reserve a returning force to a certain extent. When the measuring strip is drawn by 3 meters out of the housing and then rewound, it may be very fast rewound by the strong spring force and be rebound, causing a danger of damaging the strip itself and user's body.
Japanese Publication No. 58-15721 discloses a measure tape instrument wherein a winding reel is provided with a plate-weight that can enter into frictional engagement with a cylindrical surface of a brake drum by the action of a centrifugal force to prevent the winding reel from rotating at a speed over a certain dangerous limit.
The above-mentioned countermeasure is effective but causes an increase in the number of parts and requires an additional assembling work. There is also such a problem that, in case of rewinding a measuring strip upward stretching from the housing, the weight of the strip may be added to a winding force and, therefore, a larger braking force is required, i.e., additional countermeasure is still needed.
An attempt was made to provide a guide portion that may have frictional contact with the circumference of a conventional type winding reel, but it resulted in that the reel was considerably loaded through the constant friction with the guide portion and could not smoothly wind a measuring strip thereon. Such a problem also arose that the winding reel was seized by the guiding portion with a dirt inclusion therebetween,